Ink jet printers are well known. In general, they comprise ink jet orifices, means for delivering an ink composition to the orifices, and means for causing the ink composition to emerge from the orifices in an imagewise pattern. To be useful in ink jet printing, an ink composition must be capable of meeting an extensive list of rather stringent criteria. Among the numerous factors which are of concern are such properties of the ink composition as viscosity, surface tension, pH, density, conductivity, adhesive characteristics, wetting characteristics, drying rate and shelf life.
A wide variety of different ink formulations have been proposed heretofore for use in ink jet printing. Among the numerous ink compositions of this type are those disclosed in U.S. Pat. Nos. 3,705,043, 4,024,096, 4,070,322, 4,153,467, 4,155,768, 4,176,361, 4,197,135, 4,396,429 and 4,409,039.
It is known to employ inks in ink jet printing in which a polymeric binder and a dye are dissolved in a solvent medium containing both water and an organic solvent. (See, for example, European Patent Specification No. 0 147 257, published July 8, 1987). Inks of this type, which exhibit very good characteristics in ink jet printing, can be formulated with the use of 2-methoxyethanol or methylene chloride as solvents. However, such solvents present significant health and environmental hazards, which render their use in ink compositions undesirable in many situations.
It is toward the objective of providing a novel ink composition that meets the stringent criteria required for use in ink jet printing, but is environmentally safe, that the present invention is directed.